Study On Coupling Numerical Simulation Of Multi-physics Field In Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) has been considered as a promising alternative energy source to overcome the energy shortage because of its high energy conversion efficiency and power density, low environmental hazards and others. However, the further development of planar SOFC stack faces the challenges related to maximize the power density and minimize the non-uniform temperature distribution, which contributes to the thermal stress in the SOFC components. Hence, to overcome these above questions, these works are carried out in this thesis.A three-dimensional mathematical model coupling electrochemical kinetics with fluid dynamics was developed to simulate the transport phenomena in planar anode-supported SOFC unit such as fluid flows, heat-mass transfer. The finite volume method was employed for the calculation, which is based on the fundament conservation laws of mass, momentum, species and energy. Results of current density, potential and power density distributions for co-flow and counter-flow cases were given out.The mathematical model was constructed to describe the mass-heat transfer and electrochemical reactions during the process of the energy transition in SOFC system. The influence of the steam reforming and water-gas shift reactions on the performance parameters of SOFC with hydrocarbon fuel gas was researched. The mathematical model was solved by the FLUENT and the subroutine method. The performance data of cell such as temperature, overpotential and current density, was analyzed and compared under the different working voltage conditions.A three-dimensional mathematical thermo-fluid model coupling the electrochemical kinetics with fluid dynamics by using temperature-dependent physical parameters of multi-component mixture gas and cell stack components was developed to simulate the heat and mass transfer in a planar SOFC stack. The distributions of temperature and current density, overpotential loss and other performance parameters of the single-cell stack in various operating parameters were obtained by a commercial CFD code (Fluent) and external VC++ sub-routine based on flow uniformity analysis of air and fuel flow rates. Numerical flow data are found in good agreement with experimental results reported in the literature.On the basis of the temperature data obtained by simulating the thermo-fluid and electrochemical model, the stress and displacement in a planar SOFC stack was analyzed by using ANSYS to discuss the thermodynamics characteristics of SOFC stack. In the co-flow case, the displacement in the center area of PEN (Positive /Electrolyte/ Negative) structure is higher; the location of higher stress zone of PEN structure is close to the bolt. The maximum Von Mises stress in cathode is bigger than in anode or electrolyte because of the thick anode. The Von Mises stress and displacement decrease when the air inlet delivery rate or operating voltage increases. However, air inlet delivery rate and operating voltage are choose to optimize both of power output and thermodynamics characteristics of SOFC stack in practice.